FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention relates to an improved diaphragm-type pneumatic brake actuator
for vehicle braking systems wherein the central portion of the cup-shaped diaphragm
is maintained in surface contact with the contact surface of the piston during reciprocal
movement of the diaphragm and piston, thereby reducing frictional wear of the diaphragm,
extending the life of the diaphragm and providing improved performance of the brake
actuator. A mechanical interlock is formed between the diaphragm and the piston adjacent
the outer periphery of the piston during reciprocal movement of the piston and diaphragm
as the diaphragm is inverted by pneumatic pressure during actuation of the brake actuator,
eliminating the requirement for an adhesive.
[0002] Pneumatic brake actuators form part of the pneumatic braking system of commercial
vehicles having a large gross vehicle weight, including trucks, buses and trailers
requiring a braking system which responds rapidly with substantial braking power.
A typical diaphragm-type pneumatic brake actuator includes a housing having cup-shaped
housing members including opposed rim or flange portions, a flexible diaphragm which
is cup-shaped in its relaxed condition including a central portion, a generally conical
side wall which surrounds the central portion and a generally radial rim portion which
extends between the rim portions of the housing members. A brake actuator further
includes a piston having a contact surface which engages the central portion of the
diaphragm and which reciprocates with the central and side wall portions of the diaphragm
in response to pneumatic pressure changes on opposed sides of the diaphragm from a
first position, wherein the diaphragm is extended to a cup-shape, to a second inverted
position to actuate the vehicle braking system. The brake actuator is connected by
pneumatic lines to the pneumatic braking system of the vehicle to actuate the brake
actuator. The piston is operably connected to the braking system of the vehicle to
actuate the vehicle brakes.
[0003] There are generally two components of a brake actuator system. The first component,
commonly referred to as the service chamber, actuates the vehicle braking system under
normal braking operation. The piston in the service chamber includes a generally flat
head portion which engages the central portion of the diaphragm in the service chamber
and a piston rod which extends through an end wall of the service chamber housing.
When the brake is actuated by the vehicle operator, pneumatic pressure is received
by the service chamber housing on the side of the diaphragm opposite the piston head,
inverting the cup-shaped diaphragm and driving the piston rod through the end wall
of the service chamber housing and actuating the braking system of the vehicle. When
the vehicle operator releases the brake, a return spring located between the end wall
of the service chamber housing and the piston head, returns the piston and diaphragm
to a ready position.
[0004] A brake actuator system further includes an emergency or spring chamber having a
power spring which actuates the braking system of the vehicle when the pneumatic pressure
of the vehicle falls below a predetermined minimum or the parking brake is actuated
by the vehicle operator. In a spring brake chamber, a power spring is located in the
housing between the end wall and the piston. During normal operation of the vehicle,
the pneumatic pressure from the vehicle is received in the spring chamber on the side
of the cup-shaped diaphragm opposite the power spring and piston, thereby normally
compressing the power spring. When the pneumatic pressure in the spring chamber falls
below a predetermined minimum, the power spring expands and actuates the braking system
of the vehicle.
[0005] The spring and service chambers may be combined in a "piggyback" assembly as disclosed,
for example, in U.S. Patent No. 4,960,036 assigned to the assignee of this application,
wherein the assembly includes a central generally H-shaped flange case and the opposed
ends of the flange case are enclosed by cup-shaped housing members to define a service
chamber on one side of the flange case and a spring chamber on the opposed side of
the flange case. A central opening in the web portion of the flange case receives
a pushrod having a head portion biased against the central portion of the diaphragm
in the service chamber opposite the piston and power spring, such that the pushrod
is driven against the piston in the service chamber to actuate the vehicle braking
system when the pressure in the spring chamber falls below a predetermined minimum
pressure. Alternatively, the spring and service chambers may be utilized as separate
components of the brake actuator system as is known in the prior art.
[0006] Figure 1 illustrates the spring chamber 10 of a conventional dual diaphragm or piggyback
pneumatic brake actuator. The assembly includes a generally H-shaped flange case 12
having a central web portion 14, an outer wall 16 and a radially extending flange
18. The spring chamber 10 is enclosed by a cover or head 20 having an end wall 22,
a side wall 24 and a flange or skirt portion 26. The flange portion 26 includes a
generally radially extending portion 28, an axially extending portion 30 and a radially
inwardly extending lip 32 which is inelastically deformed as discussed further below.
The spring chamber 10 further includes a flexible diaphragm 34 described above which
includes a central portion 36, a side wall portion 38 and a radially extending rim
portion 40. The preferred shape of the diaphragm radial rim portion is further described
in U.S. Patent No. 5,992,297 assigned to the assignee of this application. As described
in the above-referenced U.S. Patent No. 4.960,036, the diaphragm 34 is assembled on
the flange case 12 with the radial rim portion 40 of the diaphragm overlying the flange
portion 18 of the flange case 12. The head 20 is then assembled on the flange case
with the radial portion 28 overlying the flange 18 of the flange case. The radial
lip 32 is then deformed radially inwardly as shown, permanently securing the head
20 to the flange case 12. The radial rim portion 40 of the diaphragm is simultaneously
compressed between the radial flange portions 18 and 28 of the flange case and head,
respectively, forming sealed pneumatic chambers 42 and 44 on opposed sides of the
diaphragm.
[0007] The spring chamber 10 further includes a piston 46 having a central portion 48 and
an annular contact portion 50 having an annular contact surface 52 which normally
engages the central portion 36 of the diaphragm. The spring chamber 10 further includes
a powerful coiled power spring 58 which is compressed between the end wall 22 of the
head and the radial portion 50 of the piston. A power spring and piston guide 60 centers
the power spring 58 in the pneumatic chamber 44 and the guide 60 includes a rolled
opening 62 which centers dome-shaped end of the piston 48 during operation of the
brake actuator as further described below. The spring chamber 10 further includes
a pushrod 64 which reciprocates through an opening 66 in the web portion 14 of the
flange case as described below. The opening 66 includes annular seals (not shown)
which prevent leakage between the pneumatic chambers 42 and 44. The pushrod 64 may
either be spring biased against the central portion 36 of the diaphragm or affixed
to the diaphragm as shown in Figure 1. In the disclosed embodiment, the pushrod 64
includes a threaded end portion 68 which is received through an opening 70 in the
central portion 36 of the diaphragm and secured to the diaphragm by nut 76. Leakage
through the diaphragm opening 70 is prevented by washer 72 and conical washer 74.
[0008] The operation of the pneumatic brake actuator 10 shown in Figure 1 may now be described.
Pneumatic pressure or gas is received through opening 78 in the side wall 16 of the
flange case, pressurizing pneumatic chamber 42. The gas pressure in pneumatic chamber
42 acts against the flexible diaphragm 34, compressing the coiled power spring 58
and driving the piston 46 upwardly in Figure 1 to be received in the power spring
and piston guide 60 as also shown in Figure 3C described below. The flexible diaphragm
is then cup-shaped and the side wall is frusto-conical or generally conical. When
the pressure in the pneumatic chamber 42 falls below a predetermined minimum, which
may occur as a result of a failure of the pneumatic braking system of the vehicle,
the power spring 58 expands, driving the pushrod 64 through the opening 66 in the
web portion 14 of the flange case 12, actuating the vehicle braking system. The chamber
24 further serves as a parking brake when the vehicle motor is turned off and the
parking brake is actuated by the operator. In a dual-diaphragm or piggyback spring
brake actuator partially shown in Figure 1, the pushrod 64 includes an end plate 80
which engages the diaphragm in the service chamber 82 (not shown) which is driven
against the piston in the service chamber 82 (not shown) actuating the vehicle braking
system as described in the above-referenced U.S. Patent No. 4,960,036. Alternatively,
the pushrod 64 may be directly connected to the vehicle braking system where the spring
chamber is separate from the service chamber. Other details of the construction and
operation of a dual-diaphragm spring brake actuator may be found in the above-referenced
U.S. Patent No. 4.960,036.
[0009] A problem with any diaphragm-type brake actuator is diaphragm wear. As described,
the diaphragm divides the brake actuator housing into two pneumatic chambers 42 and
44 on opposed sides of the diaphragm 34 and therefore the rim portion 40 must provide
a seal between the chambers for operation of the brake actuator as described above.
Thus, the diaphragm 34 is preferably formed of a rubber or rubber-like material, such
as synthetic rubber, wherein the seal is provided by compressing the opposed flange
portions 18 and 28 of the housing members against the generally radial rim portion
40 of the diaphragm to seal the chambers 42 and 44 on opposed sides of the diaphragm.
However, the diaphragm must also be sufficiently rugged to permit repeated inversion
of the cup-shaped diaphragm during braking of the vehicle. Therefore, a typical diaphragm
includes a core of a synthetic fabric material, such as a nylon net surrounded by
natural or synthetic rubber, such as neoprene. The synthetic rubber surfaces, however,
wear during normal operation of the brake actuator, potentially resulting in leakage
between the pneumatic chambers of the brake actuator.
[0010] A primary source of diaphragm wear in diaphragm-type pneumatic brake actuators is
frictional wear between the piston 46 and the diaphragm. In conventional pneumatic
brake actuators, the surface 52 of the piston which contacts the diaphragm has a width
or diameter generally equal to the width or diameter of the center portion 36 of the
diaphragm having a flat or rounded outer edge portion 54. However, when the cup-shaped
diaphragm is inverted to actuate the vehicle braking system as shown in Figure 1 and
during return of the diaphragm to its extended cup-shape, the contact surface 52 is
spaced from the central portion 36 of the diaphragm and the outer edge 54 of the piston
rubs against the inside surface of the diaphragm as the diaphragm is inverted, resulting
in frictional wear. This problem can be reduced by gluing the contact surface of the
piston to the central portion of the diaphragm to prevent separation of the piston
and the diaphragm; however, gluing or adhesive bonding is expensive and creates separate
problems, including handling and disposal problems. Further, a brake actuator must
be able to withstand extreme temperature and humidity variations during normal operation
and the adhesive may fail. Wear of the diaphragm of a service chamber creates less
of a problem because the diaphragm in the service chamber may be replaced. However,
because of the dangers inherent in opening a spring chamber, the housing components
12 and 20 of the spring chamber are now permanently secured by crimping as shown in
Figure 1 to prevent tampering and inadvertent opening of the spring chamber as described
in the above-referenced U.S. Patent No. 4,960,036. Therefore, the entire spring chamber
assembly must be replaced if the diaphragm fails.
[0011] There has, therefore, been a longstanding need to reduce frictional wear between
the piston and the diaphragm of a piston-type pneumatic brake actuator to increase
the life of brake actuators of this type which does not require adhesive bonding.
Another longstanding need is to increase the performance of the brake actuator to
provide improved braking performance without increasing the size of the brake actuator.
These and other problems have been solved by the improved brake actuator described
below.
SUMMARY OF THE INVENTION
[0012] As set forth above, the improved diaphragm-type pneumatic brake actuator of this
invention includes a mechanical interlock between the piston and the diaphragm, preferably
located at or adjacent to the outer edge of the piston, which prevents separation
of the piston and the diaphragm during inversion of the cup-shaped diaphragm, thereby
reducing or eliminating wear between the outer edge of the piston and the diaphragm.
In the most preferred embodiment of this invention, the diaphragm is releasably retained
to the piston, such that the mechanical interlock is formed only during inversion
of the cup-shaped diaphragm to simplify assembly and avoid wear of the components
of the mechanical interlock. As described below, the mechanical interlock or locking
means can take various forms and may be utilized to reduce wear of the diaphragm in
the spring or emergency chamber and the service chamber, but a tamper-resistant spring
chamber as described above and in the above-referenced U.S. Patent No. 4,960,036,
which is permanently sealed and therefore cannot be serviced, has the greatest present
need. Further, the diaphragm in the spring chamber inverts under greater force because
it is driven by the power spring resulting in greater wear of the diaphragm in the
spring chamber.
[0013] As described above, the general construction of the improved pneumatic brake actuator
for a vehicle braking system of this invention may be conventional. That is, the pneumatic
brake actuator includes an enclosed housing having housing members including opposed
flange or rim portions. The housing members are generally cup-shaped and the opposed
rim portions generally include generally radially extending mating flange portions.
In a tamper-resident spring brake actuator as described above, at least one of the
flange portions forms a skirt which is inelastically deformed around the flange portion
of the other housing member, permanently sealing the spring chamber. Alternatively,
the spring brake chamber may be permanently sealed by a separate ring-shaped clamping
element which is inelastically deformed around the flange portions of the housing
members. However, the flange portions of the service chamber are generally secured
by a conventional bolted clamp band and may thus be opened to replace the diaphragm.
[0014] The brake actuator further includes a flexible diaphragm which is cup-shaped in its
extended position, as described above, including a central portion, a generally conical
side wall portion which surrounds the central portion, and a generally radial outer
rim portion received between the flange portions of the housing members and compressed
to seal the pneumatic chambers formed on opposed sides of the flexible diaphragm.
A conventional brake actuator further includes a piston having a contact surface normally
in surface contact with the diaphragm center portion and an outer edge portion. As
described above, the diaphragm center and side wall portions invert or partially invert
and reciprocate with the piston in response to changes of pneumatic pressure in the
pneumatic chambers formed on the opposed sides of the diaphragm from a first position,
wherein the diaphragm is extended to generally a cup-shape as described above to a
second inverted position to actuate the braking system of the vehicle.
[0015] In the preferred embodiment of the improved brake actuator of this invention, the
diaphragm includes an integral radial lip or rib which receives the outer edge or
surface of the piston and releasably retains the piston in face-to-face contact as
the diaphragm is inverted or partially inverted from its extended cup-shape to a second
inverted position during actuation of the vehicle braking system. The piston may be
conventional in form, as shown in Figure 1, wherein the contact portion 50 is flat.
However, in the most preferred embodiment, the outer portion of the piston includes
an arcuate rim which extends away from the center portion of the diaphragm when the
diaphragm in the extended cup-shaped position. This configuration has several advantages.
First, the piston and diaphragm are easier to assemble. Second, the piston outer edge
does not engage the lip during normal operation of the vehicle until the braking system
of the vehicle is actuated. Third, the diaphragm generally conforms to the arcuate
shape of the contact surface including the arcuate rim as the diaphragm is inverted
and the outer edge of the rim then firmly locks into the rim on the diaphragm in a
rolling motion. In the inverted locked position, there is full face-to-face contact
between the contact face of the piston and the center portion of the diaphragm avoiding
wear of the diaphragm as described above. There are also unexpected advantages which
were discovered during testing of this configuration. First, the reduction in wear
allows the use of a thinner diaphragm, reducing the cost. More importantly, the interlock
and particularly the improved piston configuration described results in improved performance
of the brake actuator. This is because the interlocked piston and diaphragm assembly
results in a greater effective area for the diaphragm, permitting either a reduction
in the size of the brake actuator or increased performance with the same size of brake
actuator.
[0016] As set forth above, the mechanical locking means between the piston and the central
portion of the diaphragm can take several forms. For example, a circular or annular
rib on the diaphragm may be received in a circular groove in the piston instead of
mating with the outer edge of the piston as described below in regard to the most
preferred embodiment. Further, the interlock may be reversed. That is, a circular
rib may be provided on the contact surface of the piston which interlocks with either
a rib, a plurality of ribs, or a groove on the mating surface of the diaphragm. To
provide full face-to-face contact, however, the interlock is preferably located adjacent
or near the outer edge of the piston.
[0017] As set forth above, the flexible diaphragm is generally cup-shaped having a central
portion, a generally frusto-conical side wall portion, and a radial rim portion. The
radial lip or rib in the most preferred embodiment is located on an inside surface
adjacent the side wall portion of the diaphragm when the diaphragm is assembled into
the brake actuator. However, when the diaphragm is inverted and extended by the pneumatic
pressure to a cup-shape, the rib is located on an outer surface, adjacent where the
side and end walls come together. In a most preferred embodiment, wherein the piston
includes an arcuate upstanding rim described above; the lip on the diaphragm is located
adjacent to the outer surface or edge of the piston if the rim were laid flat. This
assures that the diaphragm will conform to the shape of the piston as the diaphragm
inverts to actuate the vehicle braking system. Further, the lip or rib preferably
includes a relatively steep edge to assure locking of the outer edge of the rim portion
of the diaphragm and a rounded end to reduce friction.
[0018] Other advantages and meritorious features of the improved brake actuator of this
invention will be more fully understood from the following description of the preferred
embodiment, the appended claims, and the drawings; a brief description of which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
Figure 1 is a partially cross-sectioned side view of the spring chamber of a conventional
dual diaphragm spring brake actuator described above;
Figure 2A is a side, partially cross sectioned view of the improved pneumatic brake
actuator of this invention with the diaphragm extended by pneumatic pressure to a
cup-shape and illustrating in phantom the inverted position of the diaphragm;
Figure 2B is a side, partially cross sectioned view similar to Figure 2A illustrating
the inversion of the diaphragm during actuation of the vehicle braking system;
Figure 3A is a side partially cross sectioned view of the improved flexible diaphragm
of the brake actuator of the invention; and
Figure 3B is a cross sectional partial side enlarged view of the diaphragm illustrated
in Figure 3A.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0020] As set forth above, the general construction of the improved pneumatic brake actuator
for a vehicle braking system of this invention may be conventional. That is, the improved
mechanical interlock between the piston and the diaphragm may be utilized with conventional
diaphragm-type brake actuators. Figure 2A illustrates a spring brake actuator or chamber
10, as illustrated in Figure 1 described above, including a flange case 12, a cover
or head 20, a power spring 58 and a push rod 64. No further description of these components
which are common to the conventional spring brake actuator shown in Figure 1 are necessary.
[0021] In Figure 2A, the flexible diaphragm 90 is in the extended cup-shaped position, ready
for installation in the brake actuator. As shown and described above, the diaphragm
includes a central portion 92, a side wall 94, which is generally conical, and a rim
portion 96, which is received between and compressed by the flange portions 26 and
18 of the housing components forming a lower pneumatic chamber 40 and an upper pneumatic
chamber 42 on opposed sides of the diaphragm. Pneumatic pressure is received through
port 78 in the outer wall 16 of the flange case 12, pressurizing the pneumatic chamber
40, which acts against the flexible diaphragm 90 and the piston 98 to compress the
power spring 58. The dome-shaped central portion 100 of the piston is then received
in the rolled opening 62 in the power spring and piston guide 60, centering the piston
as described above. The piston 98 further includes a contact portion 102 having an
annular contact surface 104 which is in face-to-face contact with the central portion
92 of the diaphragm because the pressure in the pneumatic chamber 40 is generally
equal to the force of the power spring 58.
[0022] In the disclosed preferred embodiment of the pneumatic brake actuator of this invention,
the contact portion 102 of the piston 98 includes an arcuate upstanding lip or rim
portion 106 having a rounded outer edge 110. As shown in Figure 2A, the arcuate lip
or rim portion 106 extends away from the central portion 92 of the diaphragm, such
that the piston 98 is not affixed or connected to the diaphragm 90 in the extended
position. The diaphragm further includes an integral annular rib or lip 110 which
is generally adjacent to, but spaced from, the outer edge 108 of the piston, but which
receives the outer edge 108 and forms a mechanical interlock as the diaphragm 90 inverts
during actuation of the vehicle emergency or parking brake as shown in phantom in
Figure 2A and further described. The annular rib 110 is spaced from the outer edge
108 a distance equal to the length of the arcuate rim 106 if the rim were extended
straight as described below.
[0023] When the gas pressure in the pneumatic chamber 42 falls below a predetermined minimum,
which may result from a failure of the pneumatic braking system of the vehicle, the
power spring expands against the radial contact portion 102 of the piston 98, which
inverts the central and side wall portions 92 and 94 respectively of the diaphragm
90 as shown in Figure 2B. As the flexible diaphragm inverts under the force of the
power spring 58, it conforms to the shape of the arcuate lip or rim 106 which increases
the effective area of the diaphragm and therefore improves the performance of the
brake actuator which can be confirmed by comparing Figures 2B and 1. Further, as the
diaphragm is inverted as shown in Figure 2B, the rounded outer edge 108 is received
beneath the annular lip or rib 110 of the diaphragm, providing a mechanical interlock
between the piston 98 and the diaphragm 90 and maintaining full face-to-face contact
between the contact surface 104 of the piston and the diaphragm, reducing or eliminating
wear of the diaphragm as described above in regard to Figure 1. As will be understood
from the above description of the operation of the pneumatic brake actuator, the expansion
of the power spring 58 and inversion of the diaphragm central and side wall portions
92 and 94, respectively, drives the push rod 64 through the opening 66 in the web
portion 14 of the flange case actuating the braking system of the vehicle.
[0024] Figures 3A and 3B illustrate a preferred embodiment of the diaphragm 90. As manufactured,
the flexible diaphragm 90 is cup-shaped as described above. The annular lip or rib
110 is then located on the inside surface of the side wall 94 as shown in Figure 3A.
However, when the diaphragm is inverted as shown by the arrow in Figure 2B, the annular
rib 110 is located on the outside surface of the side wall 94 adjacent the junction
of the side and end walls. Figure 3B illustrates a preferred embodiment of the annular
lip, which includes a sharply inclined surface 112, a gently inclined ramp surface
114 and a rounded edge 116. The sharply inclined surface 112 receives the rounded
outer edge 108 of the piston and forms an interlock with the outer edge as described
above. As will be understood, the annular lip or rib 110 may be molded on the diaphragm
from the natural or synthetic rubber material which forms the outside layers of the
diaphragm as described above.
[0025] As set forth above, the releasable mechanical interlock formed between the piston
and the diaphragm as the diaphragm is inverted to actuate the vehicle braking system
has several important advantages over the prior art including, but not limited to,
reduction in the wear of the diaphragm. Although this improvement has particular advantages
for a diaphragm-type spring brake actuator of the general type described above, the
improvements provided by this invention may also be incorporated in the service chamber
to reduce frictional wear of the diaphragm in the service chamber and improve performance.
Further, the improved pneumatic piston-type brake actuator of this invention is not
limited to any particular design of brake actuator. Also, as described above, the
mechanical interlock or locking means described herein can take various forms and
is not limited to the preferred embodiment described herein and shown in the drawings.
Finally, although the locking rib or lip is preferably integral with the diaphragm
or the piston as described above, the locking means may also be a separate element.
Therefore, while the preferred embodiment of this invention has been described so
as to enable a person of ordinary skill in this art to make and use this invention,
the description of the preferred embodiment is intended to be exemplary only.
1. A pneumatic brake actuator for a vehicle braking system comprising an enclosed housing
including cup-shaped housing members having opposed rim portions, a flexible diaphragm,
which is cup-shaped in its extended position including a central portion, a side wall
surrounding said central portion and a rim portion extending between said rim portions
of said housing members and secured therebetween in sealed relation, and a reciprocable
piston having a contact surface in surface contact with said diaphragm central portion,
said diaphragm central and side wall portions reciprocable with said piston in response
to pnematic pressure changes in said housing on opposed sides of said diaphragm from
a first position wherein said diaphragm is extended to a cup-shape to a second inverted
position to actuate said vehicle braking system, and a non-planar annular lip on said
piston adjacent an outer surface of said piston releasably retaining said central
portion of said diaphragm to said piston contact surface during reciprocal movement
of said piston and diaphragm and reducing frictional wear of said diaphragm.
2. A pneumatic brake actuator for a vehicle braking system as set forth in claim 1, wherein
said annular lip is located on said diaphragm adjacent said outer surface of said
piston, said annular lip on said diaphragm receiving said outer surface of said piston
during said reciproccal movement and forming a mechanical interlock between said central
portion of said diaphragm and said piston during said reciprocal movement thereby
reducing fricctional wear of said diaphragm.
3. A pneumatic brake actuator for a vehicle braking system as set forth in claim 2, wherein
said piston includes a generally flat portion including said contact surface and an
outer rim portion having an outer edge defining said outer surface of said piston,
and said annular lip on said diaphragm located on said generally conical side wall
of said diaphragm.
4. A pneumatic brake actuator for a vehicle braking system as set forth in claim 3, wherein
said annular rim portion of said piston includes an arcuate portion extending away
from said diaphragm central portion when said diaphragm is located in said first position
and said annular lip is located on an inner surface of said generally conical side
wall of said diaphragm when said diaphragm is inverted to said second position, said
outer edge of said piston receiving said annular lip of said piston as said piston
is reciprocated to said second inverted position forming a mechanical interlock between
said piston annular rim portion outer edge and said diaphragm annular lip.
5. A pneumatic brake actuator for a vehicle braking system comprising an enclosed housing
including housing members having opposed rim portions, a flexible diaphragm which
is cup-shaped in its extended position, including a central portion, a side wall portion
surrounding said central portion and a generally radial rim portion extending between
said rim portions of said housing members and secured therebetween in sealed relation,
and a piston having a contact surface in surface contact with said diaphragm central
portion a non-planar outer edge portion, said diaphragm central and side wall portions
reciprocable with said piston in response to pneumatic pressure changes in said housing
on opposed sides of said diaphragm from a first position, wherein said diaphragm is
extending to a cup-shape to a second inverted position to actual said vehicle braking
system, and an annular lip on said diaphragm receiving and releasably retaining said
non-planar outer edge portion of said piston as said diaphragm is reciprocated from
said first position to said second position releasably retaining said piston contact
surface in surface contact with said diaphragm central portion and reducing frictional
wear of said diaphragm.
6. A pneumatic brake actuator for a vehicle braking system as set forth in claim 5, wherein
said annular lip on said diaphragm is located on an outer surface of said diaphragm
when said diaphragm is extended to a cup-shape in said first position, and is then
located on an inside surface to receive said outer edge portion of said piston when
said diaphragm is inverted in said second position.
7. A pneumatic brake actuator for a vehicle braking system as set forth in claim 6, wherein
said piston includes a generally flat contact surface and an annular rim portion having
an outer edge defining said outer edge portion of said piston.
8. A pneumatic brake actuator for a vehicle braking system as set forth in claim 7, wherein
said piston annular rim portion includes an arcuate portion extending away from said
central portion of said diaphragm when said diaphragm is located in said first position.
9. A pneumatic brake actuator for a vehicle braking system comprising an enclosed housing
including cup-shaped housing members having opposed rim portions, a flexible diaphragm,
which is cup-shaped in its extended position including a central portion, a side wall
surrounding said central portion and a rim portion extending between said rim portions
of said housing members and secured therebetween in sealed relation, and a reciprocable
piston having a contact surface in surface contact with said diaphragm central portion,
said diaphragm central and side wall portions reciprocable with said piston in response
to pneumatic pressure changes in said housing on opposed sides of said diaphragm from
a first position wherein said diaphragm is extended to a cup-shape to a second inverted
position to actuate said vehicle braking system, and an upstanding lip portion on
said piston adjacent an outer surface of said piston releasably retaining said central
portion of said diaphragm to said piston contact surface during reciprocal movement
of said piston and diaphragm and reducing frictional wear of said diaphragm.
10. A pneumatic brake actuator for a vehicle braking system as set forth in claim 9, wherein
said upstanding lip portion is further defined as curving away from said central portion
of said diaphragm as said diaphragm is extended by pneumatic pressure in said enclosed
housing to its extended cup-shape, but which follows the contour of said diaphragm
as said diaphragm is inverted and which receives said upstanding lip portion of said
diaphragm to releasably retain said diaphragm to said piston during said reciprocal
movement.
11. A pneumatic brake actuator for a vehicle braking system as set forth in claim 10,
wherein said upstanding lip portion is located on said diaphragm adjacent said outer
surface of said piston, said upstanding lip portion on said diaphragm receiving said
outer surface of said piston during said reciprocal movement and forming a mechanical
interlock between said central portion of said diaphragm and said piston during said
reciprocal movement thereby reducing frictional wear of said diaphragm.